The invention relates to a process for automatically detecting printed marks, which are applied at regular spacings to webs, in particular made of packaging material, from among printed sections which exhibit the printed marks and separate prints, which are applied at regular spacings in the same movement path as the printed marks. The invention also relates to an apparatus for carrying out the process, having a sensor for sensing the printed sections, and having an evaluation unit which is connected to the sensor.
The handling of the packaging material is of particular importance in the case of powerful packaging machines, and the level of manual labour to be used is to be kept as low as possible. Packaging machines predominantly process packing material in the form of long material webs provided as reels. When a finishing web is used up, the new web is intended to be connected to the finishing web as far as possible without manual intervention. This ensures continuous operation of the packaging machine.
In the case of printed packaging material with recurrent printing, the relative positioning of the finishing web and new web has to be taken into consideration when the two webs are connected. This is because, if the intention is to produce uniform blanks from the web, the blanks have to be connected to one another in a correctly positioned manner. In order to produce correctly positioned connection, the material webs are provided with printed marks which are printed on the web at blank-length spacings. Mark readers which detect the marks which are being printed on and control the connecting operation by way of the detected printed marks are known.
Disadvantageously, however, separate prints which are printed on between the printed marks are likewise detected, incorrectly, as printed marks by the known mark readers if these separate prints have a similar contour to the printed marks. This may result in incorrect operation of the packaging machine.
The invention is thus based on the problem of providing an improved detection of printed marks which also functions in a fault-free manner when separate prints are applied between the printed marks in the same movement path as the printed marks.
In order to solve this problem, the process according to the invention is characterized in that the widths of the printed sections and the spacings between, in particular adjacent, printed sections are determined and, if the width and spacing essentially correspond to predetermined values, a printed section is detected as being a printed mark.
An apparatus according to the invention is characterized, in order to solve this problem, in that the evaluation unit is designed such that, by way of a sensor signal, the widths of the printed sections and the spacings between, in particular adjacent, printed sections can be determined and, if the width and spacing essentially correspond to predetermined values, it is possible for a printed section to be detected as a printed mark.
According to the invention, the width of printed sections and the following empty spaces are detected and measured and compared with input reference values.
In the case of correspondence with the reference values, a printed section is detected as being a printed mark. It is thus possible to distinguish reliably between separate prints and printed marks. In particular, it is thus possible to avoid the situation where printed sections are detected incorrectly as printed marks.
The detected printed marks are used for controlling so-called splicing operations or operations for connecting a finishing material web to a new material web. In this case, during the connecting operation, the material webs are positioned such that, in the connecting region as well, the printed marks maintain the same spacings.
Furthermore, by virtue of printed-mark detection which continues throughout operation, it is possible to achieve constant monitoring of the correct advancement speeds of the material web in relation to the initiation of cutting-off operations, e.g. for producing blanks. In particular, it is possible to counteract tolerance-induced, continuous displacement of cuts which are to be carried out, it being possible for this displacement to result in the cut moving from its correct position. Defective packs are avoided in this way.
The rotational speed of a reel which bears the finishing material web and/or new material web is preferably calculated, and set, in dependence on the degree to which a web store is filled and on the (rotational) speed of the operated machine and/or on the conveying speed of the webs. The respective reel diameter is preferably also taken into consideration here. This coupling of the rotational speed of the reel to the rotational speed of the removal machine has the advantage that the oscillatory deviations of the web store are reduced. This reduces the oscillatory accelerations and/or inertia forces in the web store, with the result that the mechanical stressing in the web is constant. A drive, e.g. a servomotor, predetermines the rotational speed of the finishing reel and/or new reel here. The servomotor is controlled taking into the consideration the oscillatory deviation and machine rotational speed and, in particular, the reel diameter, with the result that the desired reel rotational speed is set.
The remainder or length of the web which is wound up on a reel and/or the reel diameter are/is preferably determined from the angles of rotation of the reel and of a deflection roller which runs along with the web, in particular taking into consideration the circumference of the deflector roller. It is also possible to use the length of a piece of web which is drawn off from the reel and/or the displacement path of a carriage which carries along the web. The angle of rotation of the reel is sensed in this case by an angle-of-rotation sensor. It is likewise possible for the angle of rotation of the running-along deflection roller to be sensed via an angle-of-rotation sensor or a counting mechanism for counting the revolutions of the deflection roller. Furthermore, a sensor on the carrying-along carriage can be used to determine the displacement path of the carriage. These variables pass to a central computing unit, which calculates the reel diameter from the variables. This computing unit can likewise calculate, from the variables sensed, the remainder or length of the web which is wound up on a reel.